A specific allele of the T/t locus in the house mouse, tw32, is known to cause abnormalities in sperm metabolism and sperm surface components. Recent evidence in our laboratory suggests that this allele somehow advances the time of sperm penetration and pronuclear appearance. We wish to determine the specific steps prior to sperm penetration which are affected by tw32. We propose to use spermatozoa from congenic strains of mice, differing only at the T/t locus and closely linked genes, to investigate the effect of tw32 on sperm penetration of the egg investments. We will compare the distribution of sperm at the site of fertilization after insemination in vivo of B6D2F1 females by BL/6-tw32/plus and BL/6-plus/plus males. We will also study sperm function prior to penetration of the egg in an in vitro system, using an improved technique which incorporates epinephrine into the capacitation medium.